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What Causes Monsoons to Occur?


A monsoon is a seasonal change in the direction of the prevailing wind. This wind shift typically brings about a marked change in local weather. Monsoons are often associated with rainy seasons in the tropics (the areas of Earth within 23.5 degrees latitude of the equator) and the subtropics (areas between 23.5 and about 35 degrees latitude, both north and south). In these areas, life is critically dependent on the monsoon rains. A weak monsoon rainy season may cause drought, crop failures, and hardship for people and wildlife. However, heavy monsoon rains have caused massive floods that have killed thousands of people.

Many parts of the world experience monsoons to some extent. Probably the most famous are the Asian monsoons, which affect India, China, Japan, and Southeast Asia. Monsoons also impact portions of central Africa, where their rain is critical to supporting life in the area south of the Sahara Desert. Lesser monsoon circulations affect parts of the southwestern United States. These summer rainy periods bring much needed rain to the dry plateaus of Arizona and New Mexico.

Causes of monsoons

Summer monsoon

Monsoons originate from the difference between the temperatures of sea and land. Actually land reflects the rays of sun, which causes heating of the air present over the land. Now water sources (oceans) are able to absorb this heat from air, as a result air present at the top of oceans remains relatively cooler. This fact is important for the zone of Asia, because major part of Northern Hemisphere is land but southern hemisphere is ocean. In the season of summers, earth makes a perfect angle with the sun. As a result, direct sun rays strike on the land of Northern Hemisphere. Reflection of the hot sun rays causes warming of the air of northern hemisphere. This hot air rise up in the atmosphere, as a result cooler air (southern hemisphere) from the ocean rushes to the fill the gap. This cool air also brings moisture along with it. And this moisture is the reason of summer rains in the Asia. This phenomenon is known as southwest monsoon or summer monsoon. This cycle goes on, because when the moisture filled cool air causes rain, loss of moisture and energy takes place. This causes heating of air. This hot air then rises in the atmosphere and return back to the ocean, where it again losses heat and get filled up with enough moisture. After this it rushes back to the Northern Hemisphere to again replace the warm air of the land, this causes raining again. It happens in every season of summer. Monsoon winds are the major sources of rain in many countries of south Asia.

Winter monsoon

One more monsoon exists, which is named as northeast monsoon or winter monsoon. It strikes in the winter season, when sun rays are stronger at southern hemisphere. In the winter season, lands are much cooler than the oceans. So, in this case “reverse summer monsoon”‌ takes place. As a result air reverses its circulation. Warm air moves from oceans to land and cold air (cold surges) moves from land to ocean. This cold surge entrap the moisture when it passes over the tropical waters in order to release it over the northern Australia, Indonesia, Indian coast and Sri Lanka.

Importance of monsoon winds

Monsoons are extremely essential for South Asian countries like India, as economy of these agriculture-based countries mainly depends on the accurate strike of monsoon winds which cause rains. In the monsoon dependent countries, if monsoons strike before time then they cause severe floods. Likewise, if they arrive late or with less intensity, they cause drought and famine.





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